Modified catalyst supports

ABSTRACT

A process for preparing a supported catalyst system comprising the following steps:
         a. titanating a silica-containing catalyst support having a specific surface area of from 150 m 2 /g to 800 m 2 /g, preferably 280 to 600 m 2 /g, with at least one vapourised titanium compound of the general formula selected from R n Ti(OR′) m  and (RO) n Ti(OR′) m , wherein R and R′ are the same or different and are selected from hydrocarbyl groups containing from 1 to 12 carbon and halogens, and wherein n is 0 to 4, m is 0 to 4 and m+n equals 4, to form a titanated silica-containing catalyst support having at least 0.1 wt % of Ti based on the weight of the titanated silica-containing catalyst support,   b. treating the support with a catalyst activating agent, preferably an alumoxane.   c. treating the titanated support with at least one metallocene during or after step (b).

FIELD OF THE INVENTION

The invention relates to a process for preparing modified catalystsupports, in particular catalyst supports suitable for metallocenecatalyst systems.

The invention also relates to the supported catalyst system obtainedaccording to this process, the olefin polymerisation process using sucha support and the polyolefin obtained thereby.

BACKGROUND OF THE INVENTION

Metallocene catalyst systems are extensively used in a variety ofpolymerisation systems, including the polymerisation of olefins.Generally, in order to obtain the highest activity from metallocenecatalysts, it has been necessary to use them with an organoaluminoxaneactivating agent, such as methylaluminoxane (MAO). This resultingcatalyst system is generally referred to as a homogenous catalyst systemsince at least part of the metallocene or the organoaluminoxane is insolution in the polymerisation media. These homogenous catalyst systemshave the disadvantage that when they are used under slurrypolymerisation conditions, they produce polymers which stick to thereactor walls during the polymerisation process (generally referred toas “fouling”) and/or polymers having small particle size and low bulkdensity which limit their commercial utility.

Various methods have been proposed in an effort to overcome thedisadvantages of the homogenous metallocene catalyst systems. Typically,these procedures have involved the prepolymerisation of the metallocenealuminoxane catalyst system and/or supporting the catalyst systemcomponents on a porous carrier (also known as a “particulate solid” or“support”). The porous carrier is usually a silica-containing support.Another important consideration in the development of metallocenecatalysts is the yield of solid polymer that is obtained by employing agiven quantity of catalyst in a given amount of time. This is known asthe “activity” of the catalyst. There is an ongoing search formetallocene catalysts and techniques for preparing such catalysts whichgive improved activity for the polymerisation of olefins. An improvedactivity means that less catalyst needs to be used to polymerise moreolefins, thereby reducing the costs considerably, since metallocenes aremore expensive than Ziegler-Natta and chromium catalysts.

Several attempts have been made to titanate silica supports for use inmetallocene catalysed ethylene polymerisations. Jongsomjit et al.(Molecules 2005, 10, 672, Ind. Eng. Chem. Res. 2005, 44, 9059 andCatalysis Letters Vol. 100, Nos. 3-4, April 2005) discloses thetitanation of silicas for zirconocene catalysed ethylene polymerisation,wherein the support is allegedly prepared according to Conway et al. (J.Chem. Soc., Faraday Trans. J, 1989, 85(1), 71-78), such that (withoutbeing bound to theory) the titania is mixed throughout the catalystsupport. Without being bound to theory it is thought that the activityis limited, because the catalyst grains are not rendered fragile enoughto burst during polymerisation and free up active sites. In addition,the interaction of the Ti with the actives sites is not optimized.Moreover, the interaction of the MAO with the TiOH and/or SIOH isdifferent.

EP 0882 743 discloses a titanation procedure wherein the titaniumcompound is pumped as a liquid into the reaction zone where it vaporisesto titanate a supported chromium-based catalyst. This procedure isstrictly applicable to chromium catalysts (Philipp's type catalysts)i.e. only supported chromium catalysts are titanated in this way inorder to obtain shorter polymer chains during polymerisation of olefins.There is no incentive to titanate a support (which does not contain anychromium) in the same way for use in metallocene catalysed olefinpolymerisations with the hope of increasing the catalyst system'sactivity. Chromium catalysts are an entirely different class of catalystfrom metallocenes, the latter being single-site and much more sensitiveto poisons. They undergo such completely different reaction mechanismsthat polyolefins prepared with chromium catalysts and metallocenecatalysts have very different molecular structures, notably metallocenesprovide polyolefins with narrower molecular weight distributions. Inaddition, chromium catalysts after being titanated require severeactivation conditions, e.g. activation temperatures of at least 700° C.,so that the titanium compounds ignite to yield at least partially TiO₂.

Thus, a catalyst support is needed for metallocene catalysts withimproved activity, without requiring severe activation conditions orlong residence times.

An object of the present invention is to provide a new improvedsilica-containing catalyst support for metallocenes.

It is a further object of the present invention to provide supportedmetallocene catalyst systems having a higher catalytic activity.

Furthermore, it is an object of the present invention to obtainpolyolefins with a lower catalytic residue.

SUMMARY OF THE INVENTION

At least one of the objects is solved by the present invention.

The invention covers a process for preparing a supported catalyst systemcomprising the following steps, preferably in the order given:

-   -   a. titanating a silica-containing catalyst support having a        specific surface area of from 150 m²/g to 800 m²/g, preferably        280 to 600 m²/g, more preferably 280 m²/g to 400 m²/g,        preferably in an atmosphere of dry and inert gas and/or air,        preferably at at least 220° C., with at least one vapourised        titanium compound of the general formula selected from        R_(n)Ti(OR′)_(m) and (RO)_(n)Ti(OR′)_(m), wherein R and R′ are        the same or different and are selected from hydrocarbyl groups        containing from 1 to 12 carbon and halogens, and wherein n is 0        to 4, m is 0 to 4 and m+n equals 4, to form a titanated        silica-containing catalyst support having at least 0.1 wt % of        Ti based on the weight of the titanated silica-containing        catalyst support b, treating the titanated support with a        catalyst activating agent, preferably an alumoxane.    -   c. treating the titanated support with a metallocene during or        after step (b).

The supported catalyst system obtainable according to the process of theinvention (in particular according to the process of claims 1 to 7below) is also covered. It should be noted that the supported catalystsystem obtained according to this method has titanium deposited on thesurface of the silica-containing support (see FIG. 5). Furthermore, itwas observed that the catalyst support particles have a surprisinglyimproved morphology, particularly when comprising from 0.1 to 12 wt % ofTi based on the weight of the titanated silica-containing catalystsupport.

In another embodiment a supported metallocene catalyst system isprovided having a Ti content of 0.1 to 12 wt % based on the weight ofthe titanated silica-containing catalyst support, an atomic molar ratioof Ti to the transition metal M, selected from zirconium, hafnium andvanadium, (Ti/M) of 0.13 to 500 and preferably an atomic molar ratio ofCI to Ti (Cl/Ti) of less than 2.5. In a more preferred embodiment thesupported metallocene catalyst system has a Ti content of 0.1 to 10 wt %based on the weight of the titanated silica-containing catalyst support,an atomic molar ratio Ti/M of 1.3 to 420 and preferably an atomic molarratio Cl/Ti of less than 2.5.

There is also provided a process for preparing a polyethylene comprisingthe step of polymerising olefins, preferably ethylene or propylene, inthe presence of a supported catalyst system according to the invention,either in the gas phase or in the slurry phase or solely in the case ofpropylene polymerisation, in bulk. Optionally the olefin iscopolymerised with one or more alpha-olefin comonomers.

The polyolefin obtainable using the supported catalyst system obtainableaccording to the invention is covered by the invention as well.

In another embodiment, a polyolefin is provided having an atomic molarratio of Ti/M, wherein M is selected from zirconium, hafnium andvanadium, of 0.13 to 500, preferably 1.3 to 420, and preferably anatomic molar ratio of Cl/Ti of less than 2.5.

Surprisingly the catalyst support according to the invention improvesthe activity of the metallocene deposited thereon. It is thought,without being bound to theory that the titanation step according to theinvention, causes the titanium compound to be present predominantly onthe surface of the support, thereby rendering the catalyst grains morefragile, and allowing the silica-containing support to break and/orburst during polymerisation to provide even more accessible activesites. Furthermore, the distribution of the MAO and it's interactionwith TiOH and SiOH is optimized. The electronic effect of the specificTi distribution on the catalyst grain surface increases the catalystsystem's activity. The increase in activity, means less catalyticresidue remains in the final polyolefin product and the content ofvolatiles is reduced, which are both particularly interesting featuresfrom a health and safety point of view.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a comparison of the catalytic activities of themetallocene catalyst system comprising different weight percentages ofTi added according to the invention with the catalytic activity of themetallocene catalyst system without titanium for ethylene homo andcopolymerisations.

FIG. 2 represents the activation temperature profile of the metallocenecatalyst system according to the invention.

FIG. 3 represents the activation temperature profile of the metallocenecatalyst system without Titanium.

FIG. 4 represents a comparison of the catalytic activities of themetallocene catalyst system comprising 2 wt % of Ti added according tothe invention with the catalytic activity of the metallocene catalystsystem without titanium for propylene polymerisations.

FIG. 5 represents a SEM of the titanated supported catalyst system,showing the higher concentration of Ti on the surface of the particles.

DETAILED DESCRIPTION OF THE INVENTION Catalyst System

The present invention relates to a process for preparing asilica-containing catalyst support, for preparing the catalyst systemprepared with said support and for the production of polyolefins withsaid catalyst system. The support according to the invention isparticularly suitable for metallocene catalyst polymerisations, since itincreases the activity of the metallocene catalyst system considerably.

Suitable supports used in this invention are silica-based and compriseamorphous silica having a surface area of at least 150 m²/g, preferablyof at least 200 m²/g, more preferably of at least 280 m²/g, and at most800 m²/g, preferably to at most 600 m²/g, more preferably to at most 400m²/g and more preferably to at most 380 m²/g. The specific surface areais measured by N₂ adsorption using the well-known BET technique.

Silica-containing supports contain at least 20, 40, or 50% by weight ofamorphous silica. The silica-containing support may also contain one ormore of alumina, magnesia, titania, zirconia and the like.

Preferably the support is a silica support i.e. essentially 100% byweight of silica, or a silica-alumina support. In the case ofsilica-alumina supports, the support preferably comprises at most 15% byweight of alumina.

In general, the supports advantageously have a pore volume of 1 cm³/g to3 cm³/g. Supports with a pore volume of 1.3-2.0 cm³/g are preferred.Pore volume is measured by N₂ desorption using the BJH method for poreswith a diameter of less than 1000 Å. Supports with too small a porositymay result in a loss of melt index potential and in lower activity.Supports with a pore volume of over 2.5 cm³/g are less desirable becausethey may require special expensive preparation steps (e.g. azeotropicdrying) during their synthesis. In addition, because they are usuallymore sensitive to attrition during catalyst handling, activation or usein polymerisation, these supports often lead to more polymer finesproduction, which is detrimental in an industrial process.

The silica-containing support can be prepared by various knowntechniques such as but not limited to gelification, precipitation and/orspray-drying. Usually, the particle size D50 is from 5 μm, preferablyfrom 30 μm and more preferably from 35 μm, up to 150 μm, preferably upto 100 μm and most preferably up to 70 μm. D50 is defined as theparticle diameter, where 50 wt-% of particles have a smaller diameterand 50 wt-% of particles have a larger diameter. Particle size D90 is upto 200 μm, preferably up to 150 μm, most preferably up to 110 μm. D90 isdefined as the particle diameter where 90 wt-% of particles have asmaller diameter and 10 wt-% of particles have a larger diameter.Particle size D10 is at least 2 μm, preferably at least 5 μm. D10 isdefined as the particle diameter where 10 wt-% of particles have asmaller diameter and 90 wt-% of particles have a larger diameter.Particle size distribution is determined using light diffractiongranulometry, for example, using the Malvern Mastersizer 2000. Theparticle morphology is preferably microspheroidal to favour fluidisationand to reduce attrition.

The silica-containing support is dried before and/or during and/or aftertitanation. If dried before, the support can be subjected to apre-treatment in order to dehydrate it and drive off physically adsorbedwater. The dehydration step is preferably carried out by heating thecatalyst to a temperature of at least 100° C., more preferably of atleast 250° C. and most preferably of at least 270° C. The drying cantake place in an atmosphere of dry and inert gas and/or air, butpreferably in an atmosphere of dry and inert gas e.g. nitrogen. Thedrying may be carried out in a fluidised bed and in an atmosphere of adry and inert gas, for example, nitrogen. Such a dehydration step can beusually carried out for 0.5 to 6 hours. This step generally lasts for atleast 1 hour, more preferably at least 2 hours, most preferably at least4 hours.

The support can also be dried/heated after titanation, preferably to atemperature of from 350° C. to 800° C., more preferably 400° C. to 700°C., most preferably around 450° C.

The silica-containing support is loaded with one or more titaniumcompounds after or during drying. Since the aim is to provide a catalystsupport suitable for metallocene catalysts, the titanation step does notrequire the presence of chromium (the presence of chromium would implythat a chromium catalyst is being envisaged, which is not the casehere). The titanium compounds may be of the formula R_(n)Ti(OR′)_(m),(RO)_(n) Ti(OR′)_(m) and mixtures thereof, wherein R and R′ are the sameor different hydrocarbyl groups containing 1 to 12 carbon atoms orhalogen selected preferably from chlorine or fluorine, and wherein m andn is equal to 0, 1, 2, 3 or 4 and m+n equals 4. However, preferably, theCl/Ti atomic molar ratio remains below 2.5. Preferably, the titaniumcompounds are titanium tetraalkoxides Ti(OR′)₄ wherein each R′ is thesame or different and can be an alkyl or cycloalkyl group each havingfrom 3 to 5 carbon atoms. Mixtures of these compounds can also be used.Preferably, the titanium compounds are selected from Ti(OC₄H₉)₄ andTi(OC₃H₇)₄, preferably a mixture of both, more preferably a mixturehaving a weight ratio of 20:80 of Ti(OC₄H₉)₄ to Ti(OC₃H₇)₄. Thetitanation is preferably performed by progressively introducing thetitanium compound into a stream of a dry and inert non-oxidizing gas,for example, nitrogen, and/or air. More preferably, the titanation isperformed in a stream of a dry and inert gas. The titanation step iscarried out at a temperature so that titanium compound is present in itsvaporised form. The temperature is maintained preferably at at least220° C., more preferably at at least 250° C. and most preferably at atleast 270° C. The titanium compound can be pumped as a liquid into thereaction zone where it vaporizes.

This titanation step is controlled so that the total amount of depositedtitanium is from 0.1 wt % up to 60 wt % based on the weight of thetitanated silica-containing catalyst support, preferably from 0.1 wt %to 25 wt %, more preferably from 0.5 wt % to 15 wt %, even morepreferably from 1 wt % to 12 wt % and most preferably from 1 wt % to 10wt %. The total amount of titanium compound introduced into the gasstream is calculated in order to obtain the required titanium content inthe resultant catalyst support and the progressive flow rate of thetitanium compound is adjusted in order to provide a titanation reactionperiod of 0.5 to 2 hours.

Preferably, the titanation step is controlled so that the ratio of thespecific surface area of the support to titanium content of theresultant catalyst support is from 5000 to 20000 m²/g Ti, and morepreferably from 5000, 6500, 7500 or 9000 m²/g Ti, up to 12000, 15000 or20000 m²/g Ti. In a preferred embodiment, if the support has a specificsurface area of from at least 250 m²/g and of less than 380 m²/g, theratio of specific surface area of the support to titanium content of thetitanated support ranges from 5000 to 20000 m²/g Ti, and if the supporthas specific surface area of from at least 380 and of less than 400m²/g, the ratio of specific surface area of the support to titaniumcontent of the titanated catalyst support ranges from 5000 to 8000 m²/gTi.

After the introduction of the titanium compound, the catalyst supportcan be flushed under a gas stream for a period of typically 0.75 to 2hours. The dehydration and titanation steps are preferably performed inthe vapour phase in a fluidised bed.

Thereafter, the support is preferably heated to a temperature of 350° C.to 800° C., more preferably 400° C. to 700° C., most preferably around450° C. This step generally lasts for at least 1 hour, more preferablyat least 2 hours, most preferably at least 4 hours.

After titanation the titanated catalyst support can be stored under adry and inert atmosphere, for example, nitrogen, at ambient temperature.

The catalyst support is treated with a catalyst activating agent aftertitanation. In a preferred embodiment, alumoxane or a mixture ofalumoxanes are used as an activating agent for the metallocene, but anyother activating agent known in the art can be used e.g. boranecompounds. The alumoxane can be used in conjunction with the metallocenein order to improve the activity of the catalyst system during thepolymerisation reaction. As used herein, the term alumoxane is usedinterchangeably with aluminoxane and refers to a substance, which iscapable of activating the metallocene.

Alumoxanes used in accordance with the present invention compriseoligomeric linear and/or cyclic alkyl alumoxanes. In an embodiment, theinvention provides a process wherein said alumoxane has formula (III) or(IV)

R—(Al(R)—O)_(x)-AIR₂  (III) for oligomeric, linear alumoxanes; or

(—Al(R)—O—)_(y)  (IV) for oligomeric, cyclic alumoxanes

-   -   wherein x is 1-40, and preferably 10-20;    -   wherein y is 3-40, and preferably 3-20; and    -   wherein each R is independently selected from a C₁-C₈ alkyl, and        preferably is methyl.

In a preferred embodiment, the alumoxane is methylalumoxane (MAO).Generally, in the preparation of alumoxanes from, for example, aluminumtrimethyl and water, a mixture of linear and cyclic compounds isobtained. Methods for manufacturing alumoxane are known in the art andwill therefore not be disclosed in detail herein.

The treatment of the catalyst support with the alumoxane can be carriedout according to any known method known by the person skilled in theart. Advantageously, the alumoxane, preferably MAO, is mixed in an inertdiluent/solvent, preferably toluene, with the catalyst support.Alumoxane deposition preferably occurs at a temperature between 60° C.to 120° C., more preferably 80° C. to 120° C., most preferably 100 to120° C.

The catalyst support is treated with a metallocene either duringtreatment with the catalyst activating agent (1-pot method) orthereafter. Any metallocene known in the art can be applied, including amixture of different metallocenes. As used herein, the term“metallocene” refers to a transition metal complex with a coordinatedstructure, consisting of a metal atom bonded to one or more ligands. Themetallocene are used according to the invention is preferably chosenfrom formula (I) or (II):

(Ar)₂MQ₂  (I); or

R″(Ar)₂MQ₂  (II)

-   -   wherein the metallocenes according to formula (I) are        non-bridged metallocenes and the metallocenes according to        formula (II) are bridged metallocenes;    -   wherein said metallocene according to formula (I) or (II) has        two Ar bound to M which can be the same or different from each        other;    -   wherein Ar is an aromatic ring, group or moiety and wherein each        Ar is independently selected from the group consisting of        cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl,        wherein each of said groups may be optionally substituted with        one or more substituents each independently selected from the        group consisting of hydrogen, halogen and a hydrocarbyl having 1        to 20 carbon atoms and wherein said hydrocarbyl optionally        contains one or more atoms selected from the group comprising B,        Si, S, O, F and P;    -   wherein M is a transition metal M selected from the group        consisting of titanium, zirconium, hafnium and vanadium; and        preferably is zirconium;    -   wherein each Q is independently selected from the group        consisting of halogen; a hydrocarboxy having 1 to 20 carbon        atoms; and a hydrocarbyl having 1 to 20 carbon atoms and wherein        said hydrocarbyl optionally contains one or more atoms selected        from the group comprising B, Si, S, O, F and P; and    -   wherein R″ is a divalent group or moiety bridging the two Ar        groups and selected from the group consisting of a C₁-C₂₀        alkylene, a germanium, a silicon, a siloxane, an alkylphosphine        and an amine, and wherein said R″ is optionally substituted with        one or more substituents each independently selected from the        group comprising a hydrocarbyl having 1 to 20 carbon atoms and        wherein said hydrocarbyl optionally contains one or more atoms        selected from the group comprising B, Si, S, O, F and P.

The term “hydrocarbyl having 1 to 20 carbon atoms” as used herein isintended to refer to a moiety selected from the group comprising alinear or branched C₁-C₂₀ alkyl; C₃-C₂₀ cycloalkyl; C₆-C₂₀ aryl; C₇-C₂₀alkylaryl and C₇-C₂₀ arylalkyl, or any combinations thereof.

Exemplary hydrocarbyl groups are methyl, ethyl, propyl, butyl, amyl,isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl,2-ethylhexyl, and phenyl.

Exemplary halogen atoms include chlorine, bromine, fluorine and iodineand of these halogen atoms, chlorine is preferred.

Exemplary hydrocarboxy groups are methoxy, ethoxy, propoxy, butoxy, andamyloxy.

In accordance with the present invention, a process is provided whereinethylene monomer is polymerised in the presence of a bridged ornon-bridged metallocene. “Bridged metallocenes” as used herein, aremetallocenes in which the two aromatic transition metal ligands, denotedas Ar in formula (I) and (II) are covalently linked or connected bymeans of a structural bridge. Such a structural bridge, denoted as R″ informula (I) and (II) imparts stereorigidity on the metallocene, i.e. thefree movement of the metal ligands is restricted. According to theinvention, the bridged metallocene consists of a meso or racemicstereoisomer.

The two Ar can be the same or different. In a preferred embodiment thetwo Ar are both indenyl or both tetrahydroindenyl wherein each of saidgroups may be optionally substituted with one or more substituents eachindependently selected from the group consisting of hydrogen, halogenand a hydrocarbyl having 1 to 20 carbon atoms and wherein saidhydrocarbyl optionally contains one or more atoms selected from thegroup comprising B, Si, S, O, F and P. If substituted, both Ar arepreferably identically substituted. However, in a preferred embodiment,both Ar are unsubstituted.

In a preferred embodiment, the metallocene used in a process accordingto the invention is represented by formula (I) or (II) as given above,

-   -   wherein Ar is as defined above, and wherein both Ar are the same        and are selected from the group consisting of cyclopentadienyl,        indenyl, tetrahydroindenyl and fluorenyl, wherein each of said        groups may be optionally substituted with one or more        substituents each independently selected from the group        consisting of halogen and a hydrocarbyl having 1 to 20 carbon        atoms as defined herein;    -   wherein M is as defined above, and preferably is zirconium,    -   wherein Q is as defined above, and preferably both Q are the        same and are selected from the group consisting of chloride,        fluoride and methyl, and preferably are chloride; and    -   wherein R″ when present, is as defined above and preferably is        selected from the group consisting of a C₁-C₂₀ alkylene, and a        silicon, and wherein said R″ is optionally substituted with one        or more substituents each independently selected from the group        comprising a halogen, hydrosilyl, hydrocarbyl having 1 to 20        carbon atoms as defined herein.

In another preferred embodiment, the metallocene used in a processaccording to the invention is represented by formula (I) or (II) asgiven above,

-   -   wherein Ar is as defined above, and wherein both Ar are        different and are selected from the group consisting of        cyclopentadienyl, indenyl, tetrahydroindenyl and fluorenyl,        wherein each of said groups may be optionally substituted with        one or more substituents each independently selected from the        group consisting of, halogen and a hydrocarbyl having 1 to 20        carbon atoms as defined herein;    -   wherein M is as defined above, and preferably is zirconium,    -   wherein Q is as defined above, and preferably both Q are the        same and are selected from the group consisting of chloride,        fluoride and methyl, and preferably are chloride; and    -   wherein R″ when present is as defined above and preferably is        selected from the group consisting of a C₁-C₂₀ alkylene, and a        silicon, and wherein said R″ is optionally substituted with one        or more substituents each independently selected from the group        comprising a hydrocarbyl having 1 to 20 carbon atoms as defined        herein.

In an embodiment, the invention provides a process wherein saidmetallocene is an unbridged metallocene.

In a preferred embodiment, the invention provides a process wherein saidmetallocene is an unbridged metallocene selected from the groupcomprising bis(iso-butylcyclopentadienyl) zirconium dichloride,bis(pentamethylcyclopentadienyl)zirconium dichloride,bis(tetrahydroindenyl)zirconium dichloride, bis(indenyl)zirconiumdichloride, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride,bis(methylcyclopentadienyl) zirconium dichloride,bis(n-butylcyclopentadienyl)zirconium dichloride, andbis(cyclopentadienyl)zirconium dichloride; and preferably selected fromthe group comprising bis(cyclopentadienyl)zirconium dichloride,bis(tetrahydroindenyl)zirconium dichloride, bis(indenyl)zirconiumdichloride, and bis(1-methyl-3-butyl-cyclopentadienyl)zirconiumdichloride.

In another embodiment, the invention provides a process wherein saidmetallocene is a bridged metallocene.

In a preferred embodiment, the invention provides a process wherein saidmetallocene is a bridged metallocene selected from the group comprisingethylene bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, ethylenebis(1-indenyl)zirconium dichloride, dimethylsilylenebis(2-methyl-4-phenyl-inden-1-yl)zirconium dichloride, dimethylsilylenebis(2-methyl-1H-cyclopenta[α]naphthalen-3-yl)zirconium dichloride,cyclohexylmethylsilylenebis[4-(4-tert-butylphenyl)-2-methyl-inden-1-yl]zirconium dichloride,dimethylsilylenebis[4-(4-tert-butylphenyl)-2-(cyclohexylmethyl)inden-1-yl]zirconiumdichloride. Ethylene bis(4,5,6,7-tetrahydro-1-indenyl)zirconiumdichloride is particularly preferred.

In another preferred embodiment, the invention provides a processwherein said metallocene is a bridged metallocene selected from thegroup comprising diphenylmethylene (3-t-butyl-5-methyl-cyclopentadienyl)(4,6-di-t-butyl-fluorenyl) zirconium dichloride,di-p-chlorophenylmethylene (3-t-butyl-5-methyl-cyclopentadienyl)(4,6-di-t-butyl-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)(fluoren-9-yl)zirconium dichloride, dimethylmethylene(cyclopentadienyl)(2,7-ditert-butyl-fluoren-9-yl)zirconium dichloride,dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](fluoren-9-yl)zirconiumdichloride,diphenylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyp](2,7-ditert-butyl-fluoren-9-yl)zirconiumdichloride,dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](3,6-ditert-butyl-fluoren-9-yl)zirconiumdichloride dimethylmethylene (cyclopentadienyl)(fluoren-9-yl)zirconiumdichloride anddibenzylmethylene(2,7-diphenyl-3,6-di-tert-butyl-fluoren-9-yl)(cyclopentadienyl)zirconiumdichloride.

The support is treated with the metallocene, advantageously by mixingthe desired metallocene(s) with the MAO-modified support. Preferablymixing occurs at room temperature for a duration of at least 15 min,preferably at least 1 hour, more preferably at least 2 hours.

In a particular embodiment, the invention provides a process wherein themolar ratio of aluminum, provided by the alumoxane, to transition metalM, provided by the metallocene, of the polymerisation catalyst isbetween 20 and 200, and for instance between 30 and 150, or preferablybetween 30 and 100.

When the catalyst system has from 0.1 to 12 wt % of Ti based on theweight of the titanated silica-containing catalyst support, the atomicmolar ratio of Ti to the transition metal M (Ti/M), wherein M is atransition metal selected from zirconium, hafnium and vanadium, of thesupported catalyst system is of 0.13 to 500 and the atomic molar Cl/Tiratio is preferably less than 2.5. When the catalyst system of theinvention has a preferred Ti content of 1 to 10 wt % based on the weightof the titanated silica-containing catalyst support, the Ti/M atomicmolar ratio of the supported catalyst system is of 1.3 to 420.

The content of Cl, Ti and M are measured by X-ray fluorescence (XRF) asis known in the art.

The details and embodiments mentioned above in connection with theprocess for manufacturing the supported catalyst system also apply withrespect to supported catalyst system itself.

Polymerisation

The details and embodiments mentioned above in connection with theprocess for manufacturing the catalyst support and the supportedcatalyst system also apply with respect to the olefin polymerisationprocess according to the present invention.

The olefin polymerisation (which includes homo- and copolymerisations)method of the present invention is preferably carried out in the liquidphase (i.e. known as “slurry phase” or “slurry process”) or in the gasphase or in the case of propylene polymerisation also in a bulk processin the presence of the supported catalyst system according to theinvention. Combinations of different processes are also applicable.

Liquid Phase

In a slurry process (liquid phase), the liquid comprises the olefin,either propylene or ethylene, and where required one or morealpha-olefinic comonomers comprising from 2 to 10 carbon atoms, in aninert diluent. The comonomer may be selected from one or morealpha-olefins, such as ethylene (when polymerising propylene), 1-butene,1-hexene, 4-methyl 1-pentene, 1-heptene and 1-octene. Preferably, ifcopolymerising propylene, the comonomer selected is ethylene.Preferably, if copolymerising ethylene, the comonomer is selected fromone or more alpha-olefinic comonomers comprising from 3 to 10 carbonatoms, preferably 1-hexene. In either case, the inert diluent ispreferably isobutane.

The polymerisation process for ethylene is typically carried out at apolymerisation temperature of from 80 to 110° C. and under a pressure ofat least 20 bars. Preferably, the temperature ranges from 85 to 110° C.and the pressure is at least 40 bars, more preferably from 40 to 42bars.

The polymerisation process for propylene is typically carried out at apolymerisation temperature of from 60 to 110° C. and under a pressure ofat least 20 bars. Preferably, the temperature ranges from 65 to 110° C.,preferably 70° to 100° C., more preferably 65 to 78° C. and the pressureis at least 40 bars, more preferably from 40 to 42 bars.

Other compounds such as a metal alkyl or hydrogen may be introduced intothe polymerisation reaction to regulate activity and polymer propertiessuch as melt flow index. In one preferred process of the presentinvention, the polymerisation or copolymerisation process is carried outin a slurry reactor, e.g. in a liquid-full loop reactor.

Gas Phase

The catalyst system of the invention is also particularly suited for gasphase polymerisations of olefins. Gas phase polymerisations can beperformed in one or more fluidised bed or agitated bed reactors. The gasphase comprises the olefin to be polymerised, preferably ethylene orpropylene, if required one or more alpha-olefinic comonomers comprising2 to 10 carbon atoms, such as ethylene (when polymerising propylene),1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene or mixtures thereof andan inert gas such as nitrogen. Preferably, if polymerising propylene,the comonomer selected is ethylene. Preferably, if polymerisingethylene, the comonomer selected is 1-hexene. In either case, optionallya metal alkyl can also be injected in the polymerisation medium as wellas one or more other reaction-controlling agents, for example, hydrogen.Reactor temperature can be adjusted to a temperature of from 60, 65, 70,80, 85, 90 or 95° C. up to 100, 110, 112 or 115° C. (Report 1:Technology and Economic Evaluation, Chem Systems, January 1998).Optionally a hydrocarbon diluent such as pentane, isopentane, hexane,isohexane, cyclohexane or mixtures thereof can be used if the gas phaseunit is run in the so-called condensing or super-condensing mode.

Bulk

Polypropylene can also be obtained by using the metallocene catalystsystem of the invention by polymerizing propylene in a bulk process,e.g. in a loop reactor (Spheripole) or a continuous stirred-tank reactor(CSTR), or in a Spherizone® process i.e. a multi-zone circulatingreactor. Combinations of the above types of processes are alsoapplicable e.g. continuous stirred-tank reactor (CSTR) under bulkconditions, followed by a gas phase reactor. As for the slurry and gasphase process, where required, the propylene can be copolymerized withone or more alpha-olefinic comonomers comprising from 2 to 10 carbonatoms, preferably ethylene.

Increased Activity

Surprisingly, it was found that the supported catalyst system accordingto the invention greatly improves the catalytic activity of metallocenecatalyst systems.

In one embodiment, it was found that the catalytic activity of ametallocene catalyst system increased by over 40% by using the titanatedsupport according to the invention in ethylene polymerisations, ratherthan a non-titanated support. The activity of the catalyst systemincreased by over 60% when copolymerising ethylene with a comonomer. Theactivity of the catalyst system increased by over 35% when polymerisingpropylene.

Surprisingly, under industrial conditions e.g. in a double slurry loopreactor (Advanced Double Loop i.e. two slurry loop reactors connected inseries), the activities observed for homopolymerization of olefin withthe catalyst of the invention are higher than for copolymerizationprocesses under the same conditions. 100% increase in activity wasobserved.

Polyolefin

The invention also covers the polyolefin obtainable using the supportedcatalyst system of the invention. When the catalyst system of theinvention has a Ti content of 1 to 12 wt % based on the weight of thetitanated silica-containing catalyst support, the polyolefin obtainedtherewith has an atomic molar ratio of Ti to the transition metal M i.e.Ti/M, wherein M is selected from one or more of zirconium, hafnium andvanadium, of 0.13 to 500. When the catalyst system of the invention hasa Ti content of 1 to 10 wt % based on the weight of the titanatedsilica-containing catalyst support, the polyolefin obtained therewithpreferably has a Ti/M atomic molar ratio of 1.3 to 420. The transitionmetal M indicates that the polyolefin was obtained in the presence of atleast one metallocene. In addition, the Cl/Ti atomic molar ratio of thepolyolefin should be less than 2.5. This indicates that the polyolefinwas obtained in the absence of a Ziegler-Natta catalyst, sinceZiegler-Natta catalysts include large amounts of Cl. The presence of Tiindicates the use a Ti containing compound to boost catalytic activityof the metallocene.

Thus in another embodiment, the invention covers a polyolefin having aTi/M atomic molar ratio of 0.13 to 500, preferably 1.3 to 420, wherein Mis selected from one or more of zirconium, hafnium and vanadium, andpreferably a Cl/Ti atomic molar ratio of less than 2.5.

The content of Ti and M of the polyolefin are measured by inductivelycoupled plasma atomic emission spectroscopy (ICP-AES) as is known in theart. The content of Cl is measured by XRF as is known in the art. Notethat the measurements are made on the polyolefin obtained from thereactor (the fluff), prior to additivation and extrusion.

Such a Ti content allows the formation of a polyolefin using far lesscatalyst, due to the increased activity of the supported catalyst systemin the presence of Ti. As a result, the polyolefin has a lower catalyticresidue, which in turn improves its use in terms of health and safety(less catalytic residue to potentially migrate to the surface). Due tothe increased activity, the polyolefins also have lower amounts ofvolatiles, because monomer and optional comonomer are more efficientlyincorporated.

Thus the polyolefin obtained using the supported catalyst system of theinvention is particular suitable for applications requiring goodorganoleptic properties e.g. for food and drink packaging.

When polymerising ethylene, the polyethylene obtained with the catalystsystem of this invention can have a molecular weight distribution (MWD)that is represented by Mw/Mn (weight average molecular weight/numberaverage molecular weight, measured by GPC analysis) of typically from 2to 10, more typically of 3 to 8, a density measured according to ISO1183 typically from 0.920 up to 0.970 g/cm³ and a melt flow index (MI₂)measured according to ISO 1133, condition D, at 190° C. and 2.16 kgtypically from 0.1 to 50 g/10 min, preferably 0.1 to 30 g/10 min.

When polymerising propylene, the polypropylene obtained with thecatalyst system of this invention can have a density measured accordingto ISO 1183 typically from 0.920 up to 0.970 g/cm³ and a melt flow index(MI₂) measured according to ISO 1133, condition L, at 230° C. and 2.16kg, in the range from 0.05 g/10 min to 2000 g/10 min. The polyolefinsobtained using the catalyst system of the invention can be used in anyapplication known to the person skilled in the art.

The following Examples are given to illustrate the invention withoutlimiting its scope.

EXAMPLES Example 1 Ethylene Polymerisation Supported Catalyst Systems“Catalyst Z1” and “Catalyst Z2” According to the Invention 1. SupportModification

Silica support was heated under a nitrogen flow with the desired amountof Ti precursor i.e. TYSOR® a mixture of 80 wt % isopropoxide titane and20 wt % tertiary butoxide titane at 270° C., then dried at 450° C. (asshown in FIG. 1: “Catalyst Z1” having 2 wt % Ti and “Catalyst Z2” having4 wt % Ti based on the weight of the supported catalyst system). Theactivation profile for both catalysts is shown in FIG. 2.

2. MAO Treatment

MAO was mixed in toluene with the modified support at 110° C. Afterfiltration, the recovered powder was washed and dried overnight toobtain the MAO- and Ti-modified support.

3. Metallocene Treatment

The metallocene ethylene-bis(4,5,6,7-tetrahydro-1-indenyl)zirconiumdichloride was stirred with the MAO- and Ti-modified support at roomtemperature for 2 hours. After filtration, the recovered powder waswashed and dried overnight to obtain the supported catalyst systemaccording to the invention.

The obtained supported catalyst systems had:

“Catalyst Z1” a Ti content of 1.5 wt % Ti and a Ti/Zr atomic molar ratioof 3.07.

“Catalyst Z2” a Ti content of 3 wt % Ti and a Ti/Zr atomic molar ratioof 6.14.

The content of Cl was below the detection limit, only trace amountspresent.

The content of Ti, Zr and Cl were measured using XRF.

FIG. 5 shows how the Ti is deposited predominantly on the surface of theparticles.

Supported Catalyst System “Catalyst C1” (Comparative) 1. SupportModification

Silica support was dried under a nitrogen flow at 450° C.

2. MAO Treatment

MAO was mixed in toluene with the modified support at 110° C. Afterfiltration, the recovered powder was washed and dried overnight toobtain the MAO-modified support.

3. Metallocene Treatment

The metallocene ethylene-bis(4,5,6,7-tetrahydro-1-indenyl)zirconiumdichloride was stirred with the MAO-modified support at room temperaturefor 2 hours. After filtration, the recovered powder was washed and driedovernight to obtain the supported catalyst system.

Ethylene Polymerisations

Polymerisations of ethylene were carried out with “Catalysts Z1 and Z2”and compared with polymerisations of ethylene using “Catalyst C1” underthe same reaction conditions.

The catalyst system was injected in a 130 mL reactor containing 75 mL ofisobutane under an ethylene pressure of 23.8 bars at 85° C. forhomopolymerisation.

For the copolymerisation runs the same conditions were used with theaddition of 2.6 wt % of hexene.

FIG. 1 shows the comparison of the catalytic activity between thedifferent runs, “Catalyst C1” having no titanium content, being thereference. As presented, the titanation of the support according to theinvention provides increased activities. The presence of only 1.5 wt %and 3 wt % of Ti on the supported catalyst system already increases thecatalytic activity by about 40% in the case of ethylene polymerisations.

The polyethylene obtained with “Catalyst Z1” had a Ti/Zr atomic molarratio of 3.07. The polyethylene obtained with “Catalyst Z2” had a Ti/Zratomic molar ratio of 6.14.

The content of Cl was below the detection limit as measured by XRF, onlytrace amounts present. Si content was measured using XRF as well.

The content of Ti and Zr were measured using ICP-AES.

Catalytic residues were measured as follows:

PE using PE using CATALYST Z1 CATALYST C1 (invention) (comparative)Si/ppm 287.8 403 Ti/ppm 1.85 No Ti Zr/ppm 0.78 1.1

Thus the catalytic residue in the polyethylene according to theinvention using “Catalyst Z1” was less than the polyethylene obtainedusing “Catalyst C1” indicating that titanium deposited on the surface ofthe catalyst grain greatly increased the catalytic activity of themetallocene.

Polymerisations of ethylene on a ADL (Advanced Double Loop i.e. twoslurry loop reactors connected in series) process were carried out with“Catalyst Z1” and compared with results using “Catalyst C1”. “CatalystZ1” showed 100% higher catalyst activity in comparison to “Catalyst C1”.

Example 2 Propylene Polymerisation Supported Catalyst System “CatalystY” According to the Invention 1. Support Modification

Silica support was heated under a nitrogen flow with the desired amount(as shown in FIG. 4: “Catalyst Y” had 2 wt % of Ti based on the weightof the supported catalyst system) of Ti precursor, i.e. TYSOR® a mixtureof 80 wt % isopropoxide titane and 20 wt % tertiary butoxide titane, at270° C., then dried at 450° C. The activation profile is shown in FIG.2.

2. MAO Treatment

MAO was mixed in toluene with the modified support at 110° C. Afterfiltration, the recovered powder was washed and dried overnight toobtain the MAO- and Ti-modified support.

3. Metallocene Treatment

The metallocene dimethylsilylenebis(2-methyl-4-phenyl-inden-1-yl)zirconium dichloride was stirred withthe MAO- and Ti-modified support at room temperature for 2 hours. Afterfiltration, the recovered powder was washed and dried overnight toobtain the supported catalyst system according to the invention. Thecatalyst system was slurried in oil.

“Catalyst Y” had a Ti content of 1.5 wt % Ti and a Ti/Zr atomic molarratio of 18.

The content of Cl was below the detection limit, only trace amountspresent.

The content of Ti, Zr and Cl were measured using XRF.

Supported Catalyst System “Catalyst C2” (Comparative) 1. SupportModification

Silica support was dried under a nitrogen flow at 450° C.

2. MAO Treatment

MAO was mixed in toluene with the modified support at 110° C. Afterfiltration, the recovered powder was washed and dried overnight toobtain the MAO-modified support.

3. Metallocene Treatment

The metallocene dimethylsilylenebis(2-methyl-4-phenyl-inden-1-yl)zirconium dichloride was stirred withthe MAO-modified support at room temperature for 2 hours. Afterfiltration, the recovered powder was washed and dried overnight toobtain the supported catalyst system. The catalyst system was slurriedin oil.

Propylene Polymerisations

Polymerisations of propylene were carried out with “Catalyst Y”according to the invention and compared with polymerisations ofpropylene using “Catalyst C2” under the same reaction conditions.

The catalyst system was injected in a 8 L reactor containing 4.5 L ofpropylene and 1.5 NL hydrogen at 40° C. for prepolymerisation. Aftercatalyst injection, the temperature was raised to 70° C.

For the copolymerisation runs the same conditions were used with theaddition of 2.6 wt % of hexene.

FIG. 4 shows the comparison of the catalytic activity between thedifferent runs, “Catalyst C2” having no titanium content, being thereference. As presented, the titanation of the support according to theinvention provides increased activities. The presence of only 1.5 wt %of Ti on the supported catalyst system already increases the catalyticactivity by about 35% in the case of propylene polymerisations (FIG. 4).

The polypropylene obtained with “Catalyst Y” had a Ti/Zr atomic molarratio of 18. The content of Cl was below the detection limit as measuredby XRF, only trace amounts present.

The content of Ti and Zr were measured using ICP-AES.

Thus the catalytic residue in the polypropylene according to theinvention was less than the polypropylene obtained using “Catalyst C2”.

1. A process for preparing a supported catalyst system comprising thefollowing steps: a. titanating a silica-containing catalyst supporthaving a specific surface area of from 150 m²/g to 800 m²/g, preferably280 to 600 m²/g, with at least one vapourised titanium compound of thegeneral formula selected from R_(n)Ti(OR′)_(m), and (RO)_(n)Ti(OR′)_(m),wherein R and R′ are the same or different and are selected fromhydrocarbyl groups containing from 1 to 12 carbon and halogens, andwherein n is 0 to 4, m is 0 to 4 and m+n equals 4, to form a titanatedsilica-containing catalyst support having at least 0.1 wt % of Ti basedon the weight of the titanated silica-containing catalyst support, b.treating the support with a catalyst activating agent, preferably analumoxane, c. treating the titanated support with at least onemetallocene during or after step (b).
 2. The process according to claim1 wherein the catalyst support has 0.1 to 60 wt % of Ti based on theweight of the titanated silica-containing catalyst support, preferablyof from 0.5 to 25 wt %, more preferably of from 1 to 15 wt % and mostpreferably of from 1 to 12 wt %.
 3. The process according to claim 1wherein the titanium compound is selected from the group consisting oftetraalkoxides of titanium having the general formula Ti(OR′)₄ whereineach R is the same or different and can be an alkyl or cycloalkyl groupeach having from 3 to 5 carbon atoms, and mixtures thereof.
 4. Theprocess according to claim 1 wherein the titanium compounds are selectedfrom Ti(OC₄H₉)₄ and Ti(OC₃H₇)₄, preferably a mixture of both, morepreferably a mixture having a weight ratio of 20:80 of Ti(OC₄H₉)₄ toTi(OC₃H₇)₄.
 5. The process according to claim 1 wherein the metalloceneis a selected from formula (I) or (II):(Ar)₂MQ₂  (I)R″(Ar)₂MQ₂  (II) wherein the metallocenes according to formula (I) arenon-bridged metallocenes and the metallocenes according to formula (II)are bridged metallocenes; wherein said metallocene according to formula(I) or (II) has two Ar bound to M which can be the same or differentfrom each other; wherein Ar is an aromatic ring, group or moiety andwherein each Ar is independently selected from the group consisting ofcyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl, wherein eachof said groups may be optionally substituted with one or moresubstituents each independently selected from the group consisting ofhydrogen, halogen and a hydrocarbyl having 1 to 20 carbon atoms andwherein said hydrocarbyl optionally contains one or more atoms selectedfrom the group comprising B, Si, S, O, F and P; wherein M is atransition metal M selected from the group consisting of titanium,zirconium, hafnium and vanadium; and preferably is zirconium; whereineach Q is independently selected from the group consisting of halogen; ahydrocarboxy having 1 to 20 carbon atoms; and a hydrocarbyl having 1 to20 carbon atoms and wherein said hydrocarbyl optionally contains one ormore atoms selected from the group comprising B, Si, S, O, F and P; andwherein R″ is a divalent group or moiety bridging the two Ar groups andselected from the group consisting of a C₁-C₂₀ alkylene, a germanium, asilicon, a siloxane, an alkylphosphine and an amine, and wherein said R″is optionally substituted with one or more substituents eachindependently selected from the group comprising a hydrocarbyl having 1to 20 carbon atoms and wherein said hydrocarbyl optionally contains oneor more atoms selected from the group comprising B, Si, S, O, F and P.6. The process according to claim 5 wherein the metallocene is selectedfrom (I) or (II) wherein each Ar is selected independently from anindenyl or a tetrahydroindenyl, preferably each Ar being the same. 7.The process according to claim 1 wherein the alumoxane is an oligomeric,linear or cyclic alumoxane selected fromR—(Al(R)—O)_(x)—AlR₂  (III) for oligomeric, linear alumoxanes; or(—Al(R)—O—)_(y)  (IV) for oligomeric, cyclic alumoxanes wherein x is1-40; wherein y is 3-40; and wherein each R is independently selectedfrom a C₁-C₈ alkyl, preferably methyl.
 8. A supported catalyst systemobtainable according to claim
 1. 9. The supported catalyst systemaccording to claim 8 having 0.1 to 12 wt % of Ti based on the weight ofthe titanated silica-containing catalyst support and an atomic molarratio Ti/M, wherein M is a transition metal selected from one or more ofzirconium, hafnium and vanadium, of 0.13 to 500, and preferably anatomic molar ratio Cl/Ti of less than 2.5.
 10. Process for preparing apolyolefin comprising the step of polymerising an olefin in the presenceof a supported catalyst system according to claim 9 in one or more ofthe following processes: in a gas phase process, preferably in afluidized bed reactor in a slurry phase process, preferably in one ormore slurry loop reactors, more preferably in two slurry loop reactorsconnected in series
 11. Process for preparing a polypropylene comprisingthe step of polymerising propylene in the presence of a supportedcatalyst system according to claim 9, in a bulk process, preferably in aloop reactor.
 12. Process according to claim 10 wherein ethylene iscopolymerised with an alpha-olefin comonomer having from 3 to 10 carbonatoms, preferably 1-hexene.
 13. Process according to claim 10 whereinpropylene is copolymerised with an alpha-olefin comonomer having from 2to 10 carbon atoms, preferably ethylene.
 14. A polyolefin obtainableusing the supported catalyst system of claim
 9. 15. A polyolefin havingan atomic molar ratio of Ti/M of from 0.13 to 500, wherein M is atransition metal selected from one or more of zirconium, hafnium andvanadium, and an atomic molar ratio of Cl/Ti of less than 2.5.